Asbestos-laden drilling fluid and use thereof in hydraulic jet drilling



March 3, 1970 R. J. GOODWIN ET AL ASBESTOS-LADEN DRILLING FLUID AND USETHEREOF IN HYDRAULIC JET DRILLING Filed March 11, 1968 may message PUMPSA36 ale/44 0V6 uau/o 34 77 54 TMENT //V VENT 0R5 ROBERT. J. GOODW/A/W/LL/AM MEYEQ United States Patent 3,498,394 ASBESTOS-LADEN DRILLINGFLUID AND USE THEREOF IN HYDRAULIC JET DRILLING Robert J. Goodwin,Oakmont, and William K. Meyer, Indiana Township, Allegheny County, Pa.,assignors to Gulf Research & Development Company, Pittsburgh, Pa., acorporation of Delaware Filed Mar. 11, 1968, Ser. No. 711,932 Int. Cl.E21b 7/18 US. Cl. 17567 8 Claims ABSTRACT OF THE DISCLOSURE A drillingliquid capable of suspending ferrous abrasives and characterized by alow pressure drop on flowing through pipe. The drilling liquid comprisesclay solids, asbestos fibers and ferrous abrasive particles suspended inwater. To increase to an acceptable range the ability of the drillingliquid to suspend ferrous abrasive particles, the drilling liquid issheared by passing it through a nozzle at a velocity causing a pressuredrop through the nozzle of at least 4,000 psi.

This invention relates to drilling wells, and more particularly to ahydraulic jet drilling process in which a drilling liquid is dischargedat high velocities against the bottom of the borehole of a well topenetrate hard formations.

Most oil and gas wells are presently drilled by a rotary drillingprocess in which a bit rotated at the lower end of drill pipemechanically breaks particles from the bottom of the borehole. Adrilling mud is circulated down the well through the drill pipe and upthrough the annulus surrounding the drill pipe to remove cuttings fromthe borehole. Clay solids are dispersed in the drilling mud to increasethe viscosity and g l strength of the drilling mud to aid in removal ofthe cuttings from the hole. Another function of the drilling mud is tocounteract pressures existing in underground formations and prevent flowfrom those formations into the borehole during the drilling operations.Weighting agents, particularly barite, are incorporated in the drillingmud to increase its density and thereby create hydrostatic pressureadequate to overcome the formation pressure. Both the barite and clayparticles suspended in drilling muds are finely divided. Most of theparticles will pass through a 325 mesh scre n.

The conventional rotary drilling method described in the precedingparagraph allows extremely fast drilling in soft formations, but therate of drilling decreases rapidly as the hardness of the formationincreases. The slow drilling in hard formations is aggravated byincreased wear of the drill bit which makes necessary frequentinterruption of the drilling for replacement of the bit.

A drilling method that has been developed in an attempt to overcome thehigh cost of drilling hard formations is hydraulic jet drilling. Inhydraulic jet drilling, an abrasive-laden liquid is pumped down throughdrill pipe and is discharged at a velocity of preferably 650 feet persecond or more through a plurality of nozzles in a drill bit at thebottom of drill pipe. A preferred abrasive material for use in thehydraulic jet drilling process is iron or steel grit or shot having aparticle size of 10 to 80 mesh and preferably to 40 mesh. It isessential that the drilling liquid used in the hydraulic jet drillingprocess be capable of suspending the abrasive as well as the cuttingswhen circulation of the drilling liquid is interrupted while adding ajoint to the drill pipe or pulling the drill pipe to replace a drillbit. The high density and large size of the ferrous abrasives makesuspension of the abrasive particles in the drilling liquid difficult. Adrilling 3,498,394 Patented Mar. 3, 1970 liquid of suitable suspensionproperties cannot be obtained merely by the addition of clay solidswithout increasing the viscosity and gel strength of the drilling liquidto such an extent that the pressure loss in the drill pipe precludeseffective drilling by the hydraulic jet drilling method.

This invention resides in a novel hydraulic jet drilling methodanddrilling liquid in whch asbestos fibers and clay solids are suspended inan aqueous liquid passed through a nozzle at a high velocity produced bya pressure drop of the order of 4,000 pounds per square inch or moreacross the nozzle. Ferrous abrasive particles are suspended in theresultant drilling liquid which is circulated down a well and dischargedat high velocities against the bottom of the borehole to penetrate theformations being drilled. A preferred drilling liquid of this inventioncontains ground corn to reduce loss of whole drilling liquid or filtrateand to aid in suspension of the liquid.

The single figure of the drawing is a diagrammatic view, partially invertical section, of apparatus for drilling by this invention.

Referring to the drawing, a well indicated generally by referencenumeral 10 is illustrated with casing 12 set in the upper end of thewell and with open hole 14 at the lower end of the well. Drill pipe 16extends downwardly through the well substantially to the 'bottom 18 ofthe borehole. A drill bit 20 having a plurality of nozz es 22 openingthrough its lower end is connected to the lower end of drill pipe 16.

A kelly 24 connected to the upper end of drill pipe 16 extends through asuitable closure 26 and rotary table 28. Power is supplied to the rotarytable through a shaft 30 to rotate the drill pipe 16 and the drill bit20 secured to the lower end of the drill pipe.

Opening from the casing 12 below closure 26 is a line 32 extending toapparatus 34 indicated generally by the legend Drilling LiquidTreatment. A line 36 from the drilling liquid treatment apparatusdelivers drilling liquid to high-pressure pumps 38 which recirculate thedrilling liquid through a line 40 to the upper end of the kelly 24. Apair of pressure transfer cases 42 may be provided for injecting theabrasive into the high-pressure drilling liquid delivered to the upperend of kelly 24.

In the performance of the hydraulic jet drilling method of thisinvention, an aqueous suspension of asbestos fibers and clay solids isdelivered by high-pressure pumps through line 40 into the .upper end ofkelly 24. The drilling liquid passes from kelly 24 downwardly throughdrill pipe 16 into the drill bit 20 from which the drilling liquid isdischarged through nozzles 22. The high flow rate of the drillingliquidprovided by high-pressure pumps 38 causes a pressure drop acrossnozzles 22 of at least 4,000 and preferably exceeding 5,000 psi. Thehigh-velocity jets discharged from the nozzles cut the bottom 28 of theborehole, and the cuttings from the bottom of the borehole arerecirculated upwardly through the annulus between the borehole wall andthe drill pipe to the top of the well.

Drilling liquid discharged through line 32 is delivered to apparatus 34in which the drilling liquid is treated before it is recirculated in thewell. Ordinarily, the treatment consists of removing large-size cuttingsand very fine particles and cooling the liquid before passing it to thehigh-pressure pumps. After one circulation of the aqueous suspension ofasbestos and clay solids, the ferrous abrasive particles are introducedinto the suspension to form the desired drilling liquid. Theincorporation of the ferrous abrasive particles can be accomplished inthe drilling liquid treatment and the abrasive-laden drilling liquiddelivered to the high-press ure pumps 38.

Another method of incorporating the abrasives is to add the abrasiveparticles to the abrasive-free liquid discharged from the pumps 38. Suchaddition can be accomplished by means of the high-pressure transfercases 42. The abrasive-laden drilling liquid is then delivered downthrough the drill pipe and discharged through nozzles 22 to cut thebottom of the borehole. Clay solids, asbestos fiber, ferrous abrasivesand water are added to the system as required to maintain the desiredvolume of drilling mud of the desired composition.

In the hydraulic jet drilling method, the abrasive-laden drilling liquidis discharged from the drill bit at a high velocity against the bottomof the borehole in a plurality of jet streams that cut a major portionof the bottom of the borehole as the jet bit 20 is rotated. Because ofthe extremely high velocity at which the drilling liquid is dischargedfrom the drill bit and necessity of a large number of jet streams,usually 10 to 20, to cut the entire bottom of the borehole at a highrate of penetration, the flow rate in the drill pipe and annulus ishigh. Unless the drilling liquid has a unique combination of strongsolidssuspension characteristics and low-pressure drop, it cannot beused effectively in hydraulic jet drilling with ferrous abrasives. Aclay suspension having an adequate viscosity and gel strength to suspendferrous abrasive causes an excessive pressure drop in the drill pipe andannulus.

The asbestos fibers used in the drilling liquid of this invention arefinely divided fibrous particles of chrysotile. Because of the fibrousnature of the particles, they are not accurately measured by the usualscreening technique; however, particles used in the preparation of thedrilling liquid should be smaller than 10 mesh. The size of theparticles originally incorporated into the drilling liquid is not highlycritical inasmuch as the particles are separated and broken during thehydraulic jet drilling operation. After one pass through the nozzles ofthe drill bit, the drilling liquid other than the abrasive particleswill pass through a 100-rnesh screen. A typical particle size analysisof asbestos fibers suitable for use in this invention before addition tothe drilling liquid is:

On US. Sieve Series, mesh: Percent 10 1.5

Pan

Clay solids are incorporated in the aqueous suspension of aqueous fibersas a dispersing agent aiding in dispersion of the fibers in the liquid.Because of the necessity of reducing the viscosity of the drillingliquid to maintain a low pressure loss in the drill pipe and annuluswhen the drilling liquid is circulated through the well, clays such asattapulgite or some native clays are preferred to high-yield clays suchas bentonite.

The asbestos fibers are suspended in the drilling liquid in aconcentration in the range of one to four percent by weight of thedrilling liquid. The concentration of clay solids is in the range of 2to 7 percent by weight. The ratio of asbestos fibers to clay solids ispreferably in the range of 1 to 2 to 1 to 3.5.

The aqueous suspension of asbestos fiber, clay solids, and ferrousabrasives will in many instances be an adequate drilling liquid withoutfurther modification. When drilling some formations, the loss offiltrate from the drilling liquid may be excessive. To prevent excessiveloss of drilling liquid, ground corn can be added to the drilling liquidin a concentration of 1 to 4 percent by weight of the drilling liquid.The severe shear to which the drilling liquid is exposed in passingthrough the nozzles of the drill bit apparently liberates the starchfrom the ground corn and eliminates the processing steps heretoforerequired to produce the starch used in drilling muds for conventionalrotary drilling processes. In addition to reducing the filtrate loss ofthe drilling liquid, because of the presence of corn starch, the fibrousor lamellar particles of the ground corn help suspend the abrasiveparticles and aid in plugging openings in the borehole wall which mightotherwise cause loss of whole drilling liquid, as distinguished fromloss of only the liquid component of the drilling liquid. If ground cornis added to the drilling liquid, a starch preservative such as a phenylmercury compound, formaldehyde, or pentachlorophenol should be added tothe drilling liquid. While ground corn is a highly preferred additivebecause of the several beneficial effects it produces, other fluid-lossreducing additives conventionally used in drilling muds can beincorporated in the drilling liquid to reduce fluid loss.

When making up the initial drilling liquid for the hydraulic jetdrilling process, the aqueous suspension of asbestos and clay solidspreferably is circulated at least once through the drill bit to separatethe clumps of asbestos fibers and give a drilling liquid capable ofsuspending the ferrous abrasive. An alternative method is to provide asuitably valved line from the outlet of the high-pressure pump tonozzles at the surface positioned to discharge the liquid into a storagetank. Thereafter, the ferrous abrasive is added in a concentration of 1to 4 percent and preferably 1 /2 to 2 /2 percent by weight of thedrilling liquid. The ferrous abrasives used in hydraulic jet drillingare commercially available abrasives widely used in cleaning metalcastings. It is preferred that the abrasive particles have a Rockwell Chardness of at least about 55 and have a particle size in the range of10 to and preferably 20 to 40 mesh. Either cast iron or steel particlesare suitable and the particles can be either in the form of shot orgrit.

The drilling liquid used in hydraulic jet drilling is subjected tosevere shear as it passes through the nozzles in the drill bit. Many ofthe organic compounds, such as starches, gums, carboxymethyl cellulose,and acrylonitriles, that have been added to the drilling muds to thickenthem and reduce the fluid loss of the drilling mud lose theireffectiveness when subjected to the severe shear in the drill bitnozzles. In contrast, the novel drilling liquids of this invention donot possess the properties necessary to suspend ferrous abrasives untilthey have been subjected to severe shear such as occurs by passingthrough a nozzle at a velocity causing a pressure drop of 4,000 p.s.1.

To illustrate the effect of severe shearing on the properties of thedrilling muds of this invention, suspensions in water of bentonite aloneand in combination with chrysotile asbestos fiber were mixed accordingto API specifications of oil well drilling fluid materials RP-l3(b) ofNovember 1962. The mixing was accomplished in a Hamilton-Beach mixer andwas continued for 5 to 7 minutes after which the suspensions were agedabout 16 hours. Samples of the bentonite-asbestos were sheared by twopasses through a nozzle at a pressure drop of approximately 4,000 p.s.i.Starch was added to a sample of each of the sheared and unshearedbentonite-asbestos suspensions approximately one hour beforedetermination of the viscosity and suspendibility of the compositions.The compositions of the different samples in percent by weight of theWater were:

Sample A: Unsheared2 /z bentonite, 1 /2% chrysotile asbestos Sample B:Sheared2 /2% bentonite, 1 /2% chrysotile asbestos Sample C: 10%bentonite Sample D: Sample A +2% starch Sample E: Sample B +2% starchThe viscosities of the resulting suspensions were determined on a Fannviscometer. The suspendibility of the suspensions was determined bymeasuring the rate of settling of steel shot S 230 through a column ofthe drilling liquid and is reported in second required to settle adistance of one foot. Steel shot S 230 has an average diameter of 0.023inch. The 30-minute filtrate was determined by the standard API test formeasuring the rate of liquid loss of drilling muds. The suspendibilityand viscosities are reported in Table I:

The legend No in Table I indicates that there was no measurable settlingof the steel shot in the drilling liquid in a one-hour period.

An essential characteristic of the drilling liquid for a hydraulic jetdrilling process is a low pressure drop when pumped at high velocitiesthrough drill pipe. Frequently, the hard formations in which thehydraulic jet drilling method is most advantageous are at substantialdepths. If the pressure drop caused by high rates of flow of thedrilling liquid in the drill pipe and annulus is high, the powerrequirements for maintaining the necessary pressure drop across, andflow through, the drill pipe become excessive.

Each of the suspensions described above was pumped through a 17-footsection of /z-inch stainless steel pipe at controlled and measured flowrates. The pressure drop in the 17-foot section of pipe was measured.The pressure drops of the different suspensions are reported in TableII:

TABLE II Sample A Rate, gal/min: AP, p.s.i. 8.3 .317

Sample B 6.25 .66

Sample C 7.69 1.75

Sample D 6.6 .32

Sample E 10.0 .76

The drilling liquid of this invention has a unique combination ofproperties making it valuable in jet drilling operations. Asuspendibility of ferrous abrasive of at least 4 minutes per foot isessential and as high as possible is desirable. The drilling liquid ofthis invention suspended ferrous abrasive particles without measurablesettling in a one-hour period. Only after shearing does the drillingliquid have the excellent suspendibility characteristics. The shearingdoes not impair the filtrate-loss characteristics of the drillingliquid. The excellent suspendability is obtained without the highviscosity and pressure drop of suspensions of bentonite alone in water.Circulating the asbestos-laden drilling liquid in the ordinary rotarydrilling process in which the drilling liquid merely conveys rockparticles cut mechanically by the drill bit does not impart the uniqueproperties to the drilling liquid.

We claim:

1. A hydraulic jet method of drilling a well comprising mixing clay andasbestos fibers with water to form an aqueous suspension, circulatingthe suspension down the well and discharging the suspension throughnozzles of a drill bit at a rate causing a pressure drop across thenozzles of at least 4,000 p.s.i., circulating the suspension up the wellthrough the annulus around the drill pipe, mixing ferrous abrasiveparticles with the suspension circulated up the Well to form a drillingliquid, and recirculating the drilling liquid of clay, asbestos fibers,ferrous abrasive and water down the well for continued drilling, theconcentration of the clay and asbestos being adapted to cause suspensionof the abrasive particles in the drilling liquid.

2. A method as set forth in claim 1 in which the concentration of claysolids is 1 to 7 percent by weight of the water and the ratio ofasbestos to clay solids is in the range from 1 to 2 to 1 to 3.5.

3. A hydraulic jet method for drilling a borehole in hard formationscomprising delivering a drilling liquid through drill pipe anddischarging the liquid against the hard formation from a bit at the endof the drill pipe at a rate causing a pressure drop of at least 4,000p.s.i. through nozzles in the drill bit, said drilling liquid comprisingclay, ferrous abrasives, and asbestos fibers dispersed in water toprovide a drilling liquid capable of suspending the ferrous abrasiveparticles.

4. A drilling liquid comprising water, clay solids, chrysotile asbestosfibers, and ferrous abrasive particles sheared by passing through anozzle at a pressure drop in the nozzle of at least 4,000 p.s.i., saiddrilling liquid being capable of suspending ferrous abrasive S 230particles whereby the particles settle at a rate less than 15 feet perhour.

5. A drilling liquid as set forth in claim 4 containing ground corndisseminated therethrough.

6. A drilling liquid as set forth in claim 4 in which the concentrationof clay solids is in the range of 2 to 7 percent by weight of thedrilling liquid, and the concentration of the chrysotile asbestos fibersis in the range of 1 to 4 percent by weight of the drilling liquid.

7. A drilling liquid as set forth in claim 4 in which the size of theferrous abrasive particles is in the range of 10 to mesh and thechrysotile asbestos fibers pass through a -mesh screen after a singlepass through the nozzle.

8. A method of preparing drilling liquid for use in hydraulic jetdrilling of a well comprising mixing clay solids and asbestos fiberswith water to form a suspension, pumping the suspension down drill pipein the well and discharging the suspension through a drill bit at thelower end of the drill pipe at a velocity causing a pressure drop of atleast 4,000 psi. across nozzles in the drill bit, returning thesuspension to the surface and adding ferrous abrasive particles having asize in the range of 10 to 80 mesh to the drilling liquid to maintain anabrasive concentration in the range of 1 to 4 percent.

References Cited UNITED STATES PATENTS 3,245,469 4/1966 Bertness -653,384,189 5/1968 Pekarek et al. 17567 STEPHEN J. NOVOSAD, PrimaryExaminer US. Cl. X.R. 252-85

